If you want the distinguished honor of a Will Pick of the Week, here are some easy guidelines to follow:

Choose an interesting or fun topic.

Package the submission so that it's easy to figure out how to use.

Ensure that it actually works for standard user inputs.

John's PianoTuner contribution meets all three criteria. It provides a simple, intuitive user interface that displays how well-tuned your piano is. I downloaded the file, launched it in MATLAB, walked my laptop downstairs, and had meaningful data on my piano's performance in seconds.

I'll probably want to get a second opinion, but PianoTuner tells me that my keys are all falling flat. As to how it figures this out, the algorithm is about 80 lines of code embedded into the UI callback functions. It looks like there's a fast Fourier transform and a polynomial curve fit in there.

Incidentally, you can run the tool against non-piano instruments as well. I played a random song on my computer speakers and found that musicians with professional instruments do much better.